There are known a large number of conventional air conditioners serving as refrigerating apparatuses. An example of such conventional air conditioners is formed such that a compressor, a four-way selector valve, an outdoor heat exchanger, a motor-operated expansion valve, a receiver and an indoor heat exchanger are connected in this order through refrigerant pipes, as disclosed in Japanese Patent Application Laid-Open Gazette No. 8-100944. This air conditioner is designed for cooling and heating operations.
&lt;Problems to be Solved&gt;
In renewing various kinds of air conditioners including the above-mentioned air conditioner, preinstalled refrigerant pipes are sometimes used while being left in place. In such cases, if a refrigerant in a preinstalled refrigerant circuit and a refrigerant in a newly installed refrigerant circuit are the same CFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) refrigerants, the preinstalled refrigerant pipes can be used for the new refrigerant circuit without causing so much of a problem.
For newly installed refrigerant circuits, however, a HFC (hydrofluorocarbon) refrigerant for example is proposed to be substituted for the conventional CFC or HCFC refrigerant in consideration of recent environmental problems and the like.
In this case, in order that the preinstalled refrigerant pipes are used for a new refrigerant circuit while being left in place, the insides of the refrigerant pipes must be cleaned. Specifically, lubricating oil or contaminants often deposit on the inner surfaces of the preinstalled refrigerant pipes. In particular, though mineral oil is used as lubricating oil for the conventional CFC refrigerant or the like, synthetic oil is used as lubricating oil for the HFC refrigerant. Accordingly, if the mineral-type lubricating oil is left in the preinstalled refrigerant pipe, foreign substance (contamination) will occur in the newly installed refrigerant circuit. Such foreign substance may cause problems such as closure of a throttling mechanism and damage to a compressor (41).
However, any technique for cleaning the preinstalled refrigerant pipes has not yet been proposed. Therefore, there is a demand for developing a new cleaning means for cleaning the preinstalled refrigerant pipes when the preinstalled refrigerant pipes are used for a new refrigerant circuit while being left in place.
The present invention has been made in view of the above point, and has its object of providing a new pipe cleaning method and a new pipe cleaning apparatus for a preinstalled refrigerant circuit in the case of using preinstalled refrigerant pipes for a new refrigerant circuit while leaving them in place.